The invention relates to a device for application to ovens which serves to monitor the color of a commodity, in particular coffee and similar edible products, during the course of a roast.
It is of paramount importance, when roasting coffee and similar commodities on any appreciable scale, that the condition of the commodity be monitored continuously and accurately, in order to permit of terminating the roast at the right moment.
To this end, roasting ovens, and indeed ovens in general, are provided with an inspection glass through which it is possible to verify the color of the charge visually. The color of the commodity will in fact vary as the roast progresses, changing from a light shade, of green in the case of coffee, to an increasingly dark brown.
Visual control alone being insufficient in the case of coffee, the same applicant has already set forth a device (see Italian application No. 12551 A/80) capable of monitoring the color of the beans and relaying a relative signal to a processing unit. The device in question consists in a shroud type housing, offered to the inspection glass by way of its open front and secured to the surrounding panel with a flange, which accommodates photoemissive and photodetector elements the outputs of which are fed into one input of an AND gate; the remaining input of the AND gate receives the output signals from an additional set of photoemissive and photodetector elements that sense the color of a reference sample of the correctly roasted product. Utilizing such a system, the moment that the color of the roasting commodity matches the sample color, a signal will be gated by the AND circuit to shut off the oven. Operation of the device outlined above is beset by a number of problems, however, first among which is the difficulty of ensuring accurate monitoring of the color of the beans when roasting.
More exactly, the photoemitters and photodetectors are highly sensitive to changes in temperature and, given that the device is installed in such close proximity to a heat source, both become prone to error in measure commensurate with the temperature to which they are exposed.
To limit such error, the flange of the shroud is located at a suitable distance from the surface of the oven, in order to expose the interior to the surrounding atmosphere and allow a certain degree of ventilation; external cooling fins are also incorporated, together with a toroidal duct through which air is able to circulate.
Nonetheless, air cooling of this order is neither sufficiently dependable, nor adjustable to suit the different temperature levels to which the device becomes subject during the various roasting steps. Moreover, the photodetectors are connected to the AND gate by way of means designed to correct the signal according to the prevailing temperature, and such means are themselves effected by the inherent inaccuracy of the various photoelectric elements. This much said, the distance between the shroud and the inspection glass cannot be determined solely by the need to ventilate the photoelectric elements, but most also be a function of the amount of light penetrating the shroud. In effect, ambient light can modify the color of the beans tumbling against the inside surface of the inspection glass, and in consequence, the response of the photodetectors becomes affected in a manner that is unforeseeable, and, like the temperature-related errors already mentioned, in no way preventable.
Accordingly, the object of the present invention is to overcome the drawbacks outlined above.